The present invention relates to an art which is effectively applicable to a resin mold type semiconductor device and an electronic device mounting the semiconductor devices thereon.
Memory units of large-sized high-speed computers, personal computers, and the like are constituted of semiconductor memories. DRAM (Dynamic Random Access Memory) is used especially in the semiconductor memory for achieving a larger capacity.
Since a large number of DRAMs are generally used for constructing a memory unit of a large capacity, they are constructed of resin mold type semiconductor devices which are relatively low in cost. The resin mold type semiconductor devices are arranged in the DIP (Dual in-line Package), SOP (Small Out-line Package), or ZIP (Zigzag In-line Package) structure depending on the type of mounting.
A basic structure of the resin mold type semiconductor device is such that a semiconductor pellet having thereon inner leads electrically connected with external terminals (bonding pads) is hermetically sealed with a resin. The semiconductor pellet is mounted on a tab and each of the external terminals and of the inner leads are electrically connected through a bonding wire. The resin covers the semiconductor pellet, bonding wires, tab, and inner leads. The inner leads are formed integral (electrically connected) with the outer leads (outer pins) and the outer leads are arranged to stick out of the resin.
A plurality of the resin mold type semiconductor devices of the described type are mounted on a memory board (mounting board) and incorporated in a computer as a memory unit (memory module). In mounting the resin mold type semiconductor devices (DRAMs) on a memory board, the mounting area (size) of one resin mold type semiconductor device influences the packaging density. To achieve a larger capacity (or smaller size) of a memory unit, it is required to increase the packaging density.
To solve such a technical problem, it is effective to apply an art disclosed in the gazette of Japanese Laid-open Patent Publication No. 63-52498. The art described in the gazette is such as to pile up a plurality of resin mold type semiconductor devices on a module substrate in the direction perpendicular to its mounting surface. When this art is employed, since the space above the memory board to a certain height is utilized for improving the packaging density, the provision of a large-capacity memory unit can be achieved.